1. Field of the Invention
The invention relates to a fabrication process for production of a planar solid oxide fuel cell with high conductivity by reducing impedance of a solid oxide fuel cell (SOFC) membrane electrolyte assembly (MEA), in particular, to a pore array structure furnished on one or plurality of layers of anode green tapes on the utmost outside of the anode.
2. Description of the Prior Art
The operation temperature for traditional YSZ electrolyte supported cell (ESC) is in the range from 800° C. to 1000° C. Its electrolyte substrate thickness is about 150 μm to 300 μm. ESC type cell normally operates at high temperature mainly due to thick electrolyte substrate. Thus, the mainstream product is (NiO+YSZ) anode supported cell (ASC), which has electrolyte layer with YSZ as primary material and thickness is around 10 μm, and it can lower the operation temperature in the range from 650° C. to 800° C. A common ASC membrane electrolyte assembly (MEA) process is first to synthesize anode, and then conduct sintering for electrolyte and cathode. It usually takes at least three high-temperature sintering processes at about 1400° C. The multiple-stage sintering process usually will cause compositional change or deformation, so it increases cell impedance. This technology research is mainly focused on further improving the traditional MEA research program, with the anode pore array structure, can effectively reduce the gas diffusion impedance, increase output power density of batteries and provide sustainable power output. After resolving the adverse impact caused by the electrodes sintering, the SOFC power generation will be greatly enhanced.
The traditional YSZ electrolyte supported cell (ESC) is operated with temperature range between 800° C. to 1000° C. The electrolyte substrate thickness is about from 150 μm to 300 μm. Mainly due to thick electrolyte substrate, ESC type cell operates at high temperature. The mainstream product is (NiO+YSZ) anode supported cell (ASC), which has electrolyte layer (YSZ as primary material) and thickness is around 10 μm, and it can lower the operation temperature to a range from 650° C. to 800° C. A common ASC membrane electrolyte assembly (MEA) process is first to synthesize anode, and then conduct sintering for electrolyte and cathode. It usually takes at least three high-temperature sintering processes at about 1400° C. The multiple-stage sintering process would usually cause compositional change or deformation, so it increases cell impedance. The novel development for this technology is primarily to maintain the traditional manufacturing process and use a novel treatment process that can effectively solve the negative issues with multiple-stage sintering. This novel process can effectively reduce impedance, increase ion conductivity and increase SOFC power generation.
Conventional anode supported SOFC-MEA fabrication process is to use tape casting to produce electrode green tapes, adjust the thickness and the geometry of green tape substrate through lamination, produce a half-cell containing electrolyte layer and electrode supporting substrate through calcinations/sintering, and finally use screen printing technique to build cathode layer onto the half cell substrate to complete the production of the full cell. The main disadvantages of the conventional fabrication process are stability and durability, namely, reduction-oxidation cycling and/or thermal cycling, are poor.
In order to facilitate the mechanism of gas-solid phase reaction, the cathode and anode electrodes need to be produced with porosity as a basic requirement, and that will compromise the mechanical strength of the electrodes, causing subsequent cell stack assembly package subject to break and fail. The drawbacks abovementioned hinder the development of SOFC to a perfect structure. An innovative solution is in need to solve the problem.
In view of the drawbacks of the conventional art, the present invention provides an improvement to the fabrication process for the solid oxide fuel cell (SOFC) membrane electrode assembly (MEA), using tape casting to produce anode substrates. This thin strip of green tape anode is subject to a special treatment of pore array perforation, forming an anode supporting substrate by sintering, followed by screen printing/sputtering/spin coating/spray film coating fabrication process to successfully produce high quality SOFC cell with low fuel gas diffusion impedance, improving electrical conductivity of the anode side, and finally removing the insulating layer of depleted nickel layer formed on the surface of the anode through precision abrasion. It can effectively enhance the performance of SOFC unit cell.
This application is related to U.S. patent application Ser. No. 11/964,724 filed on Dec. 27, 2007 (issued as U.S. Pat. No. 7,815,843 on Oct. 19, 2010) and entitled “Process for anode treatment of SOFC-MEA to upgrade power density in performance test”, which is hereby incorporated by reference for its entirety.